Irrigation systems for watering lawns, gardens and the like provide an ideal medium for applying fertilizer or other products while irrigating. Lawns, in particular, require frequent application of fertilizer. Generally this entails purchasing bulky granular materials and distributing them with special spreading apparatus. Alternatively, one may subscribe to expensive services that dispense liquid fertilizer from tank trucks. With either of these approaches, the fertilizer is applied only a few times per season so that the nutrients are available to the lawn sporadically. Thus the use of a lawn sprinkler system to provide small amounts of fertilizer each time the sprinkler operates is highly desirable. By using a highly concentrated liquid fertilizer and metering it into the irrigation water very slowly, a moderate supply of fertilizer can last for many irrigation periods, thereby relieving the user of frequent replenishment chores while assuring the lawn or garden of regular feeding. The rate of application is not critical so that, within limits, dilution of the concentrate over its useful period is acceptable.
It is known to employ an aspirator type of meter to add a liquid agent to a liquid carrier, as typified in U.S. Pat. No. 3,060,956 to Menzie and U.S. Pat. No. 3,194,444 to Hubert. In such apparatus a small orifice is used to limit the exchange of liquid between a main stream and a reservoir. This is appropriate where the metering rate is sufficiently high to avoid using a very small orifice. A small orifice is subject to clogging by minute particles which may be present in either the main stream or in the additive. Accordingly the orifice controlled metering systems are limited, as a practical matter, to relatively high flow rates of the material from the reservoir and would not be very useful for the lawn fertilization purpose.
It is also known, as shown in U.S. Pat. No. 3,799,442 to Delmer to use a wick in drip irrigation devices where water pressure within the supply conduit forces water through a wick-filled aperture to water a plant. A key feature of that proposal is that the wick does not clog with salts or other matter. It is not apparent from Delmer or other known art that the non-clogging feature of the wick could profitably be employed in a fertilizer dispenser or the like.